Summary of Significant Accounting Policies (Reclassification of AOCI) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax provision		$ 268,967	$ 54,163	$ 99,827
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax		(1,500)	1,400	14,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on investments available-for-sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains on investments available-for-sale		200	2,700	24,000
Income from operations before income taxes		200	2,700	24,000
Income tax provision		100	900	8,400
Net of tax		100	1,800	15,600
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service cost	[1]	(400)	(400)	(100)
Actuarial gains (losses)	[1]	(2,200)	(200)	(2,500)
Income from operations before income taxes		(2,600)	(600)	(2,600)
Income tax provision		(1,000)	(200)	(1,000)
Net of tax		$ (1,600)	$ (400)	$ (1,600)

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost.